In entry into information industry, static electricity causes various problems in electronic components. In general, static electricity includes triboelectrification generated when rubbing two different objects together, and release electrification generated when objects in close contact with each other are released from each other. The static electricity can cause suction of foreign materials such as dust, electrostatic breakdown of devices, misoperation of measuring instruments, or fires. Further, it is very likely that contemporary electronic devices are temporarily or permanently damaged by static electricity.
For instance, static electricity is generated when a release film is peeled off from a pressure-sensitive adhesive layer to bond a polarizer to a liquid crystal cell during the fabrication of a liquid crystal display. Such generated static electricity affects alignment of liquid crystal within the liquid crystal display to cause defects.
Further, as polarizers are fabricated at high speeds, a breaking phenomenon of TFT IC devices occurs to result in defects of a liquid crystal display panel by static electricity that has not been generated in an existing process when a polarizer protective film is peeled off.
Although there is a method for forming an antistatic layer on an outer surface of a polarizer in order to suppress the generation of static electricity, there is a problem in that the generation of static electricity has not been fundamentally prevented since an effect of the method is insignificant. Therefore, it is necessary to impart antistatic performance to a pressure-sensitive adhesive in order to fundamentally suppress the generation of static electricity.
Although the pressure-sensitive adhesive is excellent in static electricity-preventing performance when an ionic antistatic agent is added to the pressure-sensitive adhesive to impart antistatic performance thereto, there has been a problem in that the metal surface is corroded when the pressure-sensitive adhesive comes into contact with a metal surface. Undoubtedly, a pressure-sensitive adhesive that requires antistatic properties is generally used in insulating material products from which static electricity is generated easily. However, the pressure-sensitive adhesive requiring antistatic properties is useful in a case where antistatic properties as well as corrosion resistance are required since the possibility that the pressure-sensitive adhesive is partially brought into contact with the metal surface cannot be excluded. For instance, in case of a protective film for a polarizer, in which a metallic material called a bezel is fixed to an outer surface of the polarizer with which a pressure-sensitive adhesive of the protective film has come into contact, there has been a problem in that the bezel is deteriorated by corrosion.
Methods for imparting antistatic function to a pressure-sensitive adhesive include a method for adding conductive metal powder or carbon particles to a pressure-sensitive adhesive, and a method for adding an ionic material such as a surfactant to a pressure-sensitive adhesive. However, the method for adding conductive metal powder or carbon particles to a pressure-sensitive adhesive has problems in that a large amount of conductive metal powder or carbon particles are used so as to exhibit antistatic properties and transparency of the pressure-sensitive adhesive is deteriorated accordingly. Furthermore, the method for adding surfactant has problems in that the pressure-sensitive adhesive is easily influenced by humidity, and adhesive properties of the pressure-sensitive adhesive are deteriorated due to migration of the surfactant to the surface of the pressure-sensitive adhesive.
As a method for imparting antistatic performance to a pressure-sensitive adhesive, Japanese Patent Laid-open Publication No. H5-140519 discloses a method for suppressing the generation of static electricity by adding an ethylene oxide-modified dioctyl phthalate plasticizer to a pressure-sensitive adhesive such that the pressure-sensitive adhesive is flexible. Further, Japanese Patent Laid-open Publication No. 2004-287199 discloses a method for imparting antistatic performance to a pressure-sensitive adhesive by adding an ion conductive polymer with a hydroxyl group to a pressure-sensitive adhesive.
However, these methods have problems in that the pressure-sensitive adhesive is transferred to a surface of a polarizer, adhesion properties and rheological properties are changed, and corrosion prevention cannot be controlled.
In the meantime, several methods for preparing a pressure-sensitive adhesive that does not corrode a metal layer have been suggested. Japanese Patent Laid-open Publication No. 2005-325250 discloses only a method in which components of a carboxyl group-containing copolymer pressure-sensitive adhesive is not used.
Therefore, it is necessary to further study a pressure-sensitive adhesive which is optically transparent, causes durability and reliability not to change, and simultaneously improves antistatic performance and prevents generation of corrosion although the acrylic pressure-sensitive adhesive comes into contact with a metal surface.